In order to optimally align a film with the printed circuit board image prior to its being printed in the course of producing printed circuit boards, the film is provided in the simplest case with two marker points on opposite sides and two additional holes as reference markers are drilled during drilling of the printed circuit boards, which is required in any event. Two cameras register respectively one marker with the associated reference marker, wherein the printed circuit board can be displaced in relation to the film by an electronically controlled device for bringing the markers and the associated reference markers into exact congruence. However, the exactness of such a system not only depends on the image resolution and the exactness of the displacement device. Inexactness in preparing the drilled holes unfortunately also leads to improper alignment of the printed circuit board in relation to the film, since the board is aligned in accordance with the incorrect position of the reference markers.
A method had been proposed to compensate for such statistical errors, wherein each one of the two cameras is respectively displaced sequentially along an axis to various markers and associated reference markers. The cameras register the relative positions of the markers and reference markers, forward the information to a computer which calculates the optimal position and the displacement device moves the printed circuit board accordingly in relation to the film.
The disadvantage in this method is that the cameras need to be guided with utmost precision in order not to distort the alignment results. Furthermore, the amount of required time is increased because of having to move along the marker pairs.